This invention relates to a plasma processing apparatus and, in particular, to plasma etching cleaning or chamber etching of such a plasma processing apparatus.
For forming a thin film in production of semiconductor devices, the CVD (Chemical Vapour Deposition) is known in the prior art. Further, in order to deal with higher integration such as a ultra LSI (Large Scaled Integration), the plasma CVD has been used for formation of a reliable thin insulating film or layer, such as a silicon dioxide layer of high quality. The plasma CVD processing is performed by use of a plasma processing apparatus.
The plasma processing apparatus comprises a substrate electrode and a counter electrode facing the substrate electrode with a predetermined space therebetween within a chamber. A wafer is disposed and supported on a surface of the substrate electrode. The substrate electrode is provided with an insulating cover which covers a circumferential peripheral portion of the substrate electrode. A reaction gas of a silane is introduced into the chamber, and a high frequency power is applied to the counter electrode while the substrate electrode is grounded. Thus, a glow discharge is caused between the both electrodes and generates a plasma of the reaction gas which is highly excited. Therefore, a silicon dioxide film is efficiently deposited onto the wafer but simultaneously, the reaction product adheres, as an undesired silicon layer, onto the peripheral components of electrodes, especially, the insulating cover of the substrate electrode.
After the plasma CVD apparatus is repeatedly used for forming the silicon oxide film on different wafers, the reaction product adhering accumulates to form an undesired silicon dioxide layer of an excessive thickness so that the undesired silicon oxide film peels off to obstruct the plasma discharge.
Therefore, after the plasma processing apparatus has been used for formation of the silicon oxide layer on a predetermined number of wafers, the plasma processing apparatus is subjected to a plasma etching or chamber etching to clean components within the chamber, especially, the substrate electrode and the insulating cover of the substrate electrode.
The chamber etching is performed by introducing, in place of the silane reaction gas, fluorocarbon gas into the chamber and performing the plasma processing. The fluorocarbon, for example, CF.sub.4 reacts with the silicon dioxide to form SiF.sub.4 and CO.sub.2 which are discharged out of the chamber through a gas outlet. Thus, the undesired silicon dioxide is removed.
However, the plasma processing apparatus has suffered from silicone dioxide particles peeling off the insulating cover of the substrate electrode after repeated plasma CVD processings. Here, the insulating cover is usually made of alumina (Al.sub.2 O.sub.3).
In order to resolve the problem of particles caused after repeated CVD processing, JP-A-2 70066 proposes the use of silicon carbide (SiC) for the insulating cover. According to JP-A-2 70066, the Al.sub.2 O.sub.3 insulating cover reacts with CF.sub.4 to form AlF.sub.3 which deposit onto the insulating cover during the chamber etching. Thereafter, plasma deposition is repeated and silicon dioxide layer are increased in thickness, it peels off to generate undesired particles, because AlF.sub.3 has little surface energy. On the other hand, SiC reacts with CF.sub.4 to form SiF.sub.4 and CO.sub.2 which are discharged out of the chamber through a gas outlet.
According to JP-A-2 70066, the substrate electrode is grounded during both the plasma CVD processing and the chamber etching. Therefore, the undesired silicon oxide is deposited on the insulating cover by a large amount as compared with the counter electrode during the CVD processing, but the undesired silicon oxide on the insulating cover is not easily etched as compared with that on the counter electrode during the chamber etching. Therefore, there still remains the problem of consuming much time in etching the undesired silicon oxide on the insulating cover.
In order to improve the etching rate of the chamber etching and to decrease the frequency of maintenance operation of the plasma processing apparatus, it is necessary to improve the ratio of the etching selectivity of the silicon oxide film formed during the plasma CVD processing to that of SiC.